1. Field of the Invention
The present invention generally relates to an image recording apparatus.
2. Description of the Related Art
A paper jam often occurs in a conventional image recording apparatus such as a color printer in which toner images of a plurality of colors are printed on a recording medium such as paper. A paper jam occurs, for example, when transport rollers slip during the transportation of print paper or when more than one page of the print paper is fed at a time so that the controller determines that a print medium having a length greater than a specified length is fed. When a paper jam occurs, the printing operation is stopped and the jammed paper is removed. Then, after the jammed paper is completely removed, the printing operation is resumed.
FIG. 15 is a flowchart, illustrating the operation of the conventional image recording apparatus.
An IN sensor is disposed near print engines and detects the recording medium when the recording medium is fed from a paper cassette into the recording apparatus. A WR sensor is disposed immediately upstream of the print engines and detects the leading edge of the recording medium fed into the recording apparatus, there by determining a write timing at which LED heads are energized. An OUT sensor detects that the recording medium is discharged from a fixing unit. When continuous printing is initiated, an engine controller reads the outputs of the IN sensor, WR sensor, and OUT sensor to determine time lengths during which the recording medium passes these sensors. Based on these time lengths, the controller determines a paper jam depending on whether the recording medium passes these sensors earlier or later than predetermined timings. If a paper jam has occurred, the engine controller causes the image recording apparatus to stop.
Upon signals generated from a timer, not shown, the engine controller reads the outputs of the IN sensor, WR sensor, and OUT sensor at predetermined time intervals. If the ON/OFF periods of the IN sensor, WR sensor and OUT sensor are shorter than predetermined time lengths, the printing operation is terminated. If any one of the ON/OFF periods of the IN sensor, WR sensor and OUT sensor is longer than a predetermined time length, the printing operation is stopped and the occurrence of a jam is displayed.
The flowchart in FIG. 15 will be described.
At step S1, a check is made to determine whether the output wave form of the IN sensor is normal. If the waveform is normal, the program proceeds to step S2; if the wave form is not normal, then the program proceeds to step S4. At step S2, a check is made to determine whether the output waveform of the WR sensor is normal. If the waveform is normal, the program proceeds to step S3; if the waveform is not normal, then the program proceeds to step S4. At step S3, a check is made to determine whether the output waveform of the OUT sensor is normal. If the waveform of the OUT sensor is normal, the program ends; if the waveform is not normal, then the program proceeds to step S4. At step S4, the printing operation is terminated. At step S5, the occurrence of a paper jam is displayed on a display.
As described above, when a paper jam occurs, the operation of the image recording apparatus is promptly stopped, and the jammed recording medium is removed, thereby recovering from the paper jam.
With the aforementioned conventional image recording apparatus, the transport path of the recording medium from the paper cassette to a stacker is long. Therefore, when a paper jam occurs in the middle of a printing operation, it is difficult to take out the recording medium from the apparatus.
If a paper jam occurs near the entrance or exit of the print engines where paper can be seen, the jammed paper can be taken out without difficulty. If a paper jam occurs under the developing units for black, yellow, magenta, and cyan, the recording medium cannot be seen when an upper cover is opened. Therefore, the developing units for black, yellow, magenta, and cyan have to be disassembled before taking out the jammed recording medium.
The toner deposited on the jammed recording medium has not been fused yet and therefore the toner is likely to spill from the recording medium, making it difficult to handle the jammed recording medium. Moreover, care should be taken when the developing units are replaced to their original positions. If they are misplaced, a normal image cannot be obtained.
If the jammed recording paper fails to be removed from under the developing units, the sensors of the image recording apparatus cannot detect the presence of the recording medium properly. As a result, when the respective motors are driven in rotation perform a jam-handling operation, the recording medium left under the print engines is introduced into a cold fixing unit 20 and wraps around the roller in the fixing unit, so that the paper cannot be discharged normally.